Rochester Quadrajet rebuild

[RITTER]

Well I rebuilt my first quadrajet carburetor yesterday :shock: Actaully wasn't too bad, cleaning it up took the most time. I read to epoxy the bottom side of the jet housings so I did that and sanded the metering rods with 600 grit paper to get corrosion off them. Put a new fuel filter in it and of course all the new parts that the kit came with. I installed the carburetor after I got out of work yesterday and to my surprise it fired right up. I got the idle good and all that. 😀

Now for the problem, huge decrease in power 😢 The carbuetor I removed was a computer controlled quadratjet ( which obviously had no computer hooked up to it ) it ran just fine, just got horrible gas mileage. Are there any Rochester Guru's here that can help me out :?:

 

[RITTER]

p.s. disconnect your battery when removing your steel fuel line, arching off your alternator and setting the front of your engine on fire is not fun :idea:

 

[megaladon6]

is the carb you rebuilt and installed, the same as the one you pulled? sorry, i'm just not completely clear. if the rebuild is a non-computer, what is it from?? you can usually look up the number on the side.
but i'd say you need to tune it. at least the idle mixture. but also check and adjust your timing as you do this as they "feed" off of each other. also check for any vacuum leaks, including the base plate.

 

[billyjack]

What does it have for primary metering rods and jets? If you sanded the rods, you reduced the diameter, which richened the primary side. Do you have any idea what year / engine the carb came from? If not post the carb number which should be stamped on the left side of the carb, I have quite a few reference sources for Q-jets, so I'll try to help if you can provide some info. Also, where did you set the float level? Rochesters are very sensitive to float level adjustments. I subscribe to the Doug Roe theory of Q-Jet metering;Keep the primary on the lean side for crisp response, then feed more secondary fuel for good WOT operation.

Bill

 

[Bonnewagon]

What do you mean by "power is down"? Across the board, or WOT? Also what motor is this on? Did you record the jets and rod sizes? What secondary rods? If all else is right on, did you adjust the secondary air flap?

 

[RITTER]

The carbuetor number is 17058213. I already decoded that, 1978 Chevy carburetor. My engine is a completely stock 1973 C10, the carburetor came along with the truck (they said it was the original carburetor, but that can't be true I guess since it is a '78 carb)
When I took the sand paper to the metering rods it was for like 2 seconds to get the white corrision stuff off of them, I didn't sit there and sand on them and it was 600 grit paper.

I didn't measure any of the rods or jets since they were already in the carburetor, kind of figured thats what its got.
:|
And by saying "power is down" I mean like across the board, like this thing is nuttless now :?

And no it's not the same one I removed from the engine. When I bought the truck it had this CC Quadrajet on it with nothing hooked up to it. It ran just fine just couldn't get it to stop running super rich

 

[RITTER]

Alright, I brought the slow idle mixture screws out another full turn, so they now sit at 2 1/2 turns (seems to idle a little better in gear now) but the slow idle mixture is just that, it only controls the mixture at a sitting idle right?

I took it out for a good hard test drive, the rolling WOT is just fine, secondaries open up and it gets going real good.

Its the throttle response and from a stop accelleration that is horrible.

 

[azmalibuwagon]

I'm no expert, but here are a couple of thoughts..

If you haven't done this, adjust the APT out 2 turns initially as a starting point. It will affect your acceleration.

For idle, adjust idle mixture screws for max rpm at idle, then adjust idle speed back to spec and repeat.

Maybe the primary rods and/or jets are wrong for your motor. Did you compare them to the original?

Did you blow air through all the passages to make sure they were clear?

Good luck, hope you find the problem quickly.

 

[RITTER]

I don't have an original carburetor to compare anything to.

What is APT?

I did blow air through all passages when I cleaned it.

 

[azmalibuwagon]

What about the CCC carb you had? It was running ok, right? so the rods were probably sized pretty well.

APT=Adjustable Part Throttle - It's in the bowl just in front of the float; it's the screw that controls how far down the primary rods can go into the jets. Google Image 'quadrajet adjustable part throttle' and you'll see it.

You should see if you can get a copy of either the Doug Roe or Cliff Ruggles book.